Projector

ABSTRACT

In a projection optical system comprising: two lens groups, and a curved plane mirror, wherein the projection optical system including two story structure, and having bend means for bending at least two times the light incident from an electro-optic modulator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation of application Ser. No. 12/273,196 filed Nov. 18,2008, which claims priority of Japanese Patent Application No.2008-060685, filed Mar. 11, 2008. The disclosure of these priorapplications is hereby incorporated by reference herein in its entirety.

BACKGROUND

1. Technical Field

The present invention relates to a projector.

2. Related Art

As a close-range (short-distance) projection type projector, a projectorincluding a projection system having two lens groups and one curvedmirror has been known (see JP-A-2006-235516, for example).

Since the number of curved mirror is one in the projector of the relatedart, assembling accuracy can be higher and manufacturing cost can belower than those for a projector including a plurality of curvedmirrors.

On the other hand, in recent years, there has been a demand to make aprojector more compact.

SUMMARY

An advantage of some aspects of the invention is to provide a projectormore compact than those of related art.

A projector of an aspect of the invention includes an illuminationsystem that emits an illumination light flux, an electro-optic modulatorthat modulates the light from the illumination system in accordance withimage information, and a projection system that projects the lightmodulated by the electro-optic modulator. The projection system includesa first lens group including a plurality of lenses, the lens opticalaxis of the plurality of lenses shifted from the central axis of animage formation area of the electro-optic modulator in a firstdirection; a second lens group including a plurality of lenses, thesecond lens group disposed on the light-exiting side of the first lensgroup; a curved mirror disposed on the light-exiting side of the secondlens group; and a reflective light guiding system disposed along theoptical path between the first lens group and the curved mirror, thereflective light guiding system reflecting the light from the first lensgroup in a predetermined direction containing a second direction that isopposite the first direction as a vector component and guiding the lightto the curved mirror. The reflective light guiding system includes atleast two reflection elements, and each of the at least two reflectionelements has a flat reflection plane.

According to the projector of the aspect of the invention, since thereflective light guiding system including at least two reflectionelements is disposed along the optical path between the first lens groupand the curved mirror, the light from the first lens group can be bentat least twice and guided to the curved mirror. As a result, the spacein which the projection system is disposed can be reduced (more compact)as compared to a case, for example, in the configuration of a projectorof related art, where the light from the first lens group is not bent atall but directly guided to the curved mirror, whereby the projector canbe more compact.

The space in which the projection system is disposed can also be reduced(more compact) as compared to the space required in related art, as willbe described later in detail in a comparative example, by disposing areflective light guiding system along the optical path between the firstlens group and the curved mirror, the reflective light guiding systemreflecting the light from the first lens group in a third directiondifferent from the first and second directions (for example, when thefirst direction is oriented downward and the second direction isoriented upward, the third direction is oriented sideward with respectto the direction in which the light travels) and guiding the reflectedlight to the curved mirror. In this case, however, since the curvedmirror is disposed in a position shifted in the first direction from theelectro-optic modulator (first lens group), part of the light reflectedoff the curved mirror may disadvantageously hit an optical system(including from illumination system to projection system) and othercomponents. To prevent the light reflected off the curved mirror fromhitting the optical system, for example, the location where the opticalsystem and other components are disposed must be changed, which is notpreferable because the degrees of freedom in product design are reduced.

In contrast, since the projector according to the aspect of theinvention includes the reflective light guiding system that reflects thelight from the first lens group in a predetermined direction containingthe second direction as a vector component and guides the reflectedlight to the curved mirror, the curved mirror is disposed in a positionshifted from the electro-optic modulator (first lens group) in thesecond direction. The light reflected off the curved mirror will nottherefore hit the optical system, and it is possible to achieve aprojector in which a large number of degrees of freedom are available inproduct design.

In the projector according to the aspect of the invention, since theplurality of reflection elements that form the reflective light guidingsystem have flat reflection planes, the structure of the reflectivelight guiding system is simpler and the reflection elements can besmaller than in a case where the reflection planes are curved. Such anadvantage contributes to reduction in size of the product.

In the projector according to the aspect of the invention, it ispreferable that the optical axis of the first lens group does notintersect the optical axis of the curved mirror.

A projector configured in such a way that the optical axis of the firstlens group intersects the optical axis of the curved mirror is, forexample, a projector including a reflective light guiding system thatreflects the light from the first lens group in the third direction andguides the reflected light to the curved mirror as described above. Inthis case, however, as described above, the degrees of freedom inproduct design are disadvantageously reduced.

In contrast, since the projector according to the aspect of theinvention is configured in such a way that the optical axis of the firstlens group does not intersect the optical axis of the curved mirror, itis possible to achieve a projector in which a large number of degrees offreedom are available in product design.

In the projector according to the aspect of the invention, it ispreferable that two of the optical axis of the first lens group, theoptical axis of the second lens group, and the optical axis of thecurved mirror are present in the same plane, and the one remainingoptical axis is not present in the plane.

Such a configuration allows the space in the projector to be effectivelyused and the projector to be more compact, readily prevents the lightreflected off the curved mirror from hitting the optical system, andallows a projector in which a large number of degrees of freedom areavailable in product design to be achieved.

In the projector according to the aspect of the invention, it ispreferable that the reflective light guiding system is configured as aunit structure in which the at least two reflection elements areintegrated.

Such a configuration allows the apparatus to be readily assembled.

In the projector according to the aspect of the invention, it ispreferable that each of the first lens group and the second lens groupis configured as a unit structure in which the plurality of lenses areintegrated.

Such a configuration allows the apparatus to be readily assembled.

In the projector according to the aspect of the invention, it ispreferable that the reflective light guiding system includes a firstreflection element disposed between the first lens group and the secondlens group, the first reflection element reflecting the light from thefirst lens group in the second direction, and a second reflectionelement disposed between the first reflection element and the secondlens group or between the second lens group and the curved mirror.

Such a configuration allows a projector that is more compact and has alarger number of degrees of freedom in product design than related artto be readily achieved.

In the projector according to the aspect of the invention, it ispreferable that the reflective light guiding system includes a firstreflection element disposed between the first lens group and the secondlens group, the first reflection element reflecting the light from thefirst lens group in the second direction; a second reflection elementdisposed between the first reflection element and the second lens groupin such a way that a normal to the reflection plane of the secondreflection element is perpendicular to a normal to the reflection planeof the first reflection element; and a third reflection element disposedbetween the second reflection element and the second lens group, thethird reflection element reflecting the light from the second reflectionelement toward the second lens group.

Such a configuration allows a projector that is more compact and has alarger number of degrees of freedom in product design than related artto be readily achieved.

In the projector according to the aspect of the invention, it ispreferable that each of the reflection elements in the reflective lightguiding system is a reflection mirror or a reflection prism.

Such a configuration allows the light from the first lens group to bereliably guided to the curved mirror. Further, when the reflectionelements are reflection mirrors, the manufacturing cost of the projectorcan be reduced as compared to a case where the reflection elements arereflection prisms.

In the projector according to the aspect of the invention, it ispreferable that the curved mirror is a concave mirror.

Although the curved mirror can be, for example, a convex mirror, theabove configuration allows the product height of the projector to belower than in a case where the curved mirror is a convex mirror.

Further, (1) In a projection optical system comprising:

-   a plurality of lens groups, and-   a curved plane mirror,-   wherein the projection optical system including two story structure,    and having a plurality of plane mirrors that bends at least two    times the light incident from a color combining system disposed    upstream of the light path.    (2) The projection optical system comprising:-   first lens group, first plane mirror, second lens group, second    plane mirror, and curved mirror from upstream to downstream of the    light path in the order.    (3) The projection optical system comprising:-   first lens group, firs plane mirror, second plane mirror, second    lens group, and curved mirror from upstream to downstream of the    light path in the order.    (4) The projection optical system comprising:-   first lens group, first plane mirror, second lens group, second    plane mirror, third lens group, and curved mirror from upstream to    downstream of the light path in the order.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is an overall perspective view showing the optical system of aprojector 1000 according to a first embodiment.

FIG. 2 is a top view showing part of the optical system from anillumination optical system 100 to a cross dichroic prism 500.

FIGS. 3A and 3B explain a projection system 600.

FIGS. 4A to 4D explain the relationship between a projection image IMGprojected on a screen SCR and reflective type of liquid crystal panels400R, 400G, and 400B.

FIG. 5 is an overall perspective view showing the optical system of aprojector 1000 a according to the comparative example.

FIG. 6 explains the projector 1000 a according to the comparativeexample.

FIG. 7 explains the projector 1000 according to the first embodiment.

FIG. 8 is an overall perspective view showing the optical system of aprojector 1002 according to a second embodiment.

FIGS. 9A and 9B explain a projection system 602.

FIG. 10 is an overall perspective view showing the optical system of aprojector 1004 according to a third embodiment.

FIGS. 11A and 11B explain a projection system 604.

FIG. 12 is an overall perspective view showing the optical system of aprojector 1006 according to a fourth embodiment.

FIGS. 13A and 13B explain a projection system 606.

FIGS. 14A to 14D explain the relationship between a projection image IMGprojected on a screen SCR and reflective type of liquid crystal panels400R, 400G, and 400B in the second to fourth embodiments.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Projectors according to some aspects of the invention will be describedwith reference to embodiments shown in the drawings.

First Embodiment

In a first embodiment, a case where a reflective light guiding systemincludes three reflection elements is described. In the followingdescription, a “first direction” is oriented downward, and a “seconddirection” is oriented upward.

First, the configuration of a projector according to the firstembodiment will be described with reference to FIGS. 1 to 3.

FIG. 1 is an overall perspective view showing the optical system of aprojector 1000 according to the first embodiment. FIG. 2 is a top viewshowing part of the optical system from an illumination system 100 to across dichroic prism 500. FIGS. 3A and 3B explain a projection system600. FIG. 3A is a top view showing the projection system 600 (viewedfrom the z (+) direction), and FIG. 3B is a side view showing theprojection system 600 (viewed from the x (−) direction).

In FIG. 1, a plurality of lenses that form a first lens group 610 and asecond lens group 620 are abstractly illustrated.

In the following description, three directions perpendicular to oneanother are called a y direction (the direction along the central axisof light that exits from the cross dichroic prism 500), an x direction(the horizontal direction perpendicular to the y direction), and a zdirection (the vertical direction perpendicular to the y direction). Thedownward direction (first direction) represents the “z (−) direction,”and the upward direction (second direction) represents the “z (+)direction.”

The projector 1000 according to the first embodiment includes, as shownin FIG. 1, an illumination system 100 from which an illumination lightflux is outputted, a color separation/light guiding system 200 thatseparates the illumination light flux from the illumination system 100into red, green, and blue three color light beams and guides theseparated color light beams to areas to be illuminated, three reflectivetype of liquid crystal panels 400R, 400G, and 400B as electro-opticmodulators that modulate the three color light beams separated by thecolor separation/light guiding system 200 in accordance with imageinformation, a cross dichroic prism 500 as a color combining system thatcombines the color light beams modulated by the three reflective type ofliquid crystal panels 400R, 400G, and 400B, and a projection system 600that projects the light combined by the cross dichroic prism 500 on ascreen SCR or other projection planes.

The illumination system 100 includes, as shown in FIGS. 1 and 2, a lightsource 110 that emits illumination light flux toward the areas to beilluminated, a first lens array 120 having a plurality of first lenslets122 that divide the illumination light flux emitted from the lightsource 110 into a plurality of sub-light fluxes, a second lens array 130having a plurality of second lenslets 132 that correspond to theplurality of first lenslets 122 in the first lens array 120, apolarization conversion element 140 that converts the sub-light fluxesfrom the second lens array 130 into substantially one type of linearlypolarized sub-light fluxes having an aligned polarization direction andoutputs the linearly polarized sub-light fluxes, a superimposing lens150 that superimposes the sub-light fluxes outputted from thepolarization conversion element 140 on the areas to be illuminated, anda reflection mirror 160 that reflects the light from the superimposinglens 150 toward a color separation system 210 in the colorseparation/light guiding system 200.

The light source 110 includes an ellipsoidal reflector 114, an arc tube112, the emission center of which is located in the vicinity of a firstfocal point of the ellipsoidal reflector 114, a sub-mirror 116 thatreflects the light emitted from the arc tube 112 toward the areas to beilluminated back toward the arc tube 112, and a concave lens 118 thatoutputs the converging light from the ellipsoidal reflector 114 assubstantially parallel light. The light source 110 emits a light fluxhaving an illumination optical axis 100 ax as the central axis.

The arc tube 112 includes a lamp body and a pair of sealed portionsextending from both sides of the lamp body. The lamp body is made ofquartz glass and has a spherical shape. The lamp body has a pair ofelectrodes disposed in the lamp body and mercury, a rare gas, and atrace of halogen encapsulated in the lamp body. Various arc tubes can beemployed as the arc tube 112, such as a metal-halide lamp, ahigh-pressure mercury lamp, and an ultrahigh-pressure mercury lamp.

The ellipsoidal reflector 114 includes a tubular neck-shaped portioninto which one of the sealed portions of the art tube 112 is insertedand bonded, and a reflective concave plane that reflects the lightemitted from the art tube 112 toward a second focus position.

The sub-mirror 116 is a reflection element disposed in such a way thatit covers approximately half of the lamp body of the arc tube 112 andfaces the concave reflection plane of the ellipsoidal reflector 114. Theother sealed portion of the arc tube 112 is inserted and bonded to thesub-mirror 116. The sub-mirror 116 returns the portion of the lightemitted from the arc tube 112 that is not directed toward theellipsoidal reflector 114 back to the arc tube 112 and onto theellipsoidal reflector 114.

The concave lens 118 is disposed on the illuminated area side of theellipsoidal reflector 114 and configured to output the light from theellipsoidal reflector 114 toward the first lens array 120.

The first lens array 120 serves as a light flux dividing optical elementthat divides the light from the concave lens 118 into a plurality ofsub-light fluxes, and includes a plurality of first lenslets 122arranged in a matrix formed of multiple rows and multiple columns in aplane perpendicular to the illumination optical axis 100 ax. Althoughnot illustrated, the outer shape of each of the first lenslets 122 issimilar to the outer shape of an image formation area of each of theliquid crystal panels 400R, 400G, and 400B.

The second lens array 130 in conjunction with the superimposing lens 150has a function of focusing the images of the first lenslets 122 in thefirst lens array 120 in the vicinity of the image formation area of eachof the reflective type of liquid crystal panels 400R, 400G, and 400B.The second lens array 130 has substantially the same configuration asthat of the first lens array 120 and includes a plurality of secondlenslets 132 arranged in a matrix formed of multiple rows and multiplecolumns in a plane perpendicular to the illumination optical axis 100ax.

The polarization conversion element 140 converts the polarizationdirections of the sub-light fluxes divided by the first lens array 120into an aligned polarization direction and outputs substantially onetype of linearly polarized sub-light fluxes.

The polarization conversion element 140 includes a polarizationseparation layer that transmits the portion of the illumination lightflux from the light source 110 that has one polarization component(P-polarized component, for example) and reflects the portion of theillumination light flux that has the other polarization component(S-polarized component, for example) in the direction perpendicular tothe illumination optical axis 100 ax, a reflection layer that reflectsthe light having the other polarization component that has beenreflected off the polarization separation layer in the directionparallel to the illumination optical axis 100 ax, and a retardationplate that converts the light having the one polarization component thathas passed through the polarization separation layer into light havingthe other polarization component.

The superimposing lens 150 is an optical element that collects theplurality of sub-light fluxes that have passed through the first lensarray 120, the second lens array 130, and the polarization conversionelement 140 and superimposes the sub-light fluxes in the vicinity of theimage formation area of each of the reflective type of liquid crystalpanels 400R, 400G, and 400B. The superimposing lens 150 is disposed insuch a way that the optical axis of the superimposing lens 150substantially coincides with the illumination optical axis 100 ax of theillumination system 100. The superimposing lens 150 may be a compoundlens comprised of a combination of a plurality of lenses.

The reflection mirror 160 is disposed in such a way that a normal to thereflection plane thereof is inclined by 45 degrees to the optical axisof the superimposing lens 150. The thus disposed reflection mirror 160reflects the light that exits from the superimposing lens 150 (lightoriented in the x (−) direction) in the y (+) direction.

The color separation/light guiding system 200 includes a colorseparation system 210, reflection mirrors 220 and 260, a dichroic mirror230, and polarizing beam splitters 240, 250, and 270. The colorseparation/light guiding system 200 has a function of separating thelight reflected off the reflection mirror 160 (the illumination lightflux that has exited from the illumination system 100) into red, green,and blue three color light beams and guiding the color light beams tothe respective three reflective type of liquid crystal panels 400R,400G, and 400B, which are illumination target.

The color separation system 210 includes two color separation filters,each of which having a wavelength selecting film formed on a substrate,the wavelength selecting film reflecting a light flux in a predeterminedwavelength range and transmitting a light flux in the other wavelengthrange. The color separation system 210 separates the light reflected offthe reflection mirror 160 into light having a blue light component andlight having the other color light components (red and green lightcomponents).

The light having a blue light component separated by the colorseparation system 210 is reflected off the reflection mirror 260 andincident on the polarizing beam splitter 270 via a converging lens 300B.Since the illumination light flux from the illumination system 100 hasbeen converted by the polarization conversion element 140 intosubstantially one type of linearly polarized sub-light fluxes having analigned polarization direction, the light passing through the converginglens 300B passes through the polarizing beam splitter 270 and isincident on the reflective type of liquid crystal panel for blue light400B. The converging lens 300B is provided to convert the sub-lightfluxes from the illumination system 100 into light fluxes substantiallyparallel to the respective principal rays. The other converging lenses300R and 300G are configured in the same manner as the converging lens300B.

The polarizing beam splitter 270 is a plate-type polarizing beamsplitter and has a polarization separation film provided on alight-transmissive substrate. The polarizing beam splitter 270 has afunction of transmitting light having one polarization component andreflecting light having the other polarization components. The otherpolarizing beam splitters 240 and 250 are configured in the same manneras the polarizing beam splitter 270.

The light reflected off the reflective type of liquid crystal panel forblue light 400B reaches the polarizing beam splitter 270. The light thathas been modulated by the reflective type of liquid crystal panel 400Bso that the polarization direction is rotated is reflected off thepolarizing beam splitter 270 and reaches the cross dichroic prism 500.On the other hand, the light that has not been modulated by thereflective type of liquid crystal panel 400B so that the polarizationdirection is not rotated passes through the polarizing beam splitter270. That is, such light does not reach the cross dichroic prism 500.

The light having color light components other than the blue lightcomponent separated by the color separation system 210 is reflected offthe reflection mirror 220 and incident on the dichroic mirror 230.

The dichroic mirror 230 is an optical element having a wavelengthselecting film formed on a substrate, the wavelength selecting filmreflecting a light flux in a predetermined wavelength range andtransmitting a light flux in the other wavelength range. The dichroicmirror 230 is a mirror that reflects the green light component andtransmits the red light component.

The light having the green light component reflected off the dichroicmirror 230 passes through the converging lens 300G and the polarizingbeam splitter 250 and is incident on the reflective type of liquidcrystal panel for green light 400G. On the other hand, the light havingthe red light component passing through the dichroic mirror 230 passesthrough the converging lens 300R and the polarizing beam splitter 240and is incident on the reflective type of liquid crystal panel for redlight 400R.

The reflective type of liquid crystal panels 400R, 400G, and 400B areillumination targets illuminated by the illumination system 100 andmodulate the illumination light flux in accordance with imageinformation. Each of the reflective type of liquid crystal panels 400R,400G, and 400B is a wide-vision reflective type of liquid crystal panelin which its image formation area has an aspect ratio of 16:9, andincludes, although not illustrated, a light transmissive substrate (ITO)having a light-transmissive electrode, a drive circuit substrate havinga pixel electrode, a liquid crystal layer encapsulated and sealedbetween the light-transmissive substrate and the drive circuitsubstrate, and orientation films respectively disposed between thelight-transmissive electrode and the liquid crystal layer and betweenthe liquid crystal layer and the pixel electrode.

Heat dissipating fins 410R, 410G, and 410B are disposed on thereflective type of liquid crystal panels 400R, 400G, and 400B.

Polarization plate 420R, 420G, and 420B are disposed in front of thecross dichroic prism 500.

The cross dichroic prism 500 is an optical element that combines opticalimages based on respective modulated color light beams that have exitedthrough the polarization plates 420R, 420G, and 420B to form a colorimage. The cross dichroic prism 500 is formed by bonding fourrectangular prisms and thus has a substantially square shape when viewedfrom above. Dielectric multilayer films are formed on the substantiallyX-shaped interfaces between these bonded rectangular prisms. Thedielectric multilayer film formed on one of the substantially X-shapedinterfaces reflects the blue light, whereas the dielectric multilayerfilm formed on the other interface reflects the red light. Thesedielectric multilayer films bend the blue light and the red light, whichthen travel in the same direction as the green light, so that the threecolor light beams are combined and the combined light is outputtedtoward the projection system 600.

The projection system 600 includes, as shown in FIGS. 1 and 3, a firstlens group 610 having a plurality of lenses (ten or more lenses, forexample), a second lens group 620 having a plurality of lenses (twolenses, for example) and disposed on the light-exiting side of the firstlens group 610, a curved mirror 630 disposed on the light-exiting sideof the second lens group 620, and a reflective light guiding system 640disposed along the optical path from the first lens group 610 to thesecond lens group 620.

Although not illustrated, each of the first lens group 610 and thesecond lens group 620 is configured as a unit structure in which aplurality of lenses are integrated, and can be adjusted on a unit basisin terms of layout position and angle. The lenses that form each of thelens groups are configured as a unit with the lenses therein adjusted interms of position and angle.

The plurality of lenses that form each of the first lens group 610 andthe second lens group 620 are plastic lenses. Lenses L1 and L2 that formthe second lens group 620 are shaped in such a way that part of thelenses L1 and L2 on the upper (z(+) direction) side with respect to thelens optical axis thereof is cut away. To fabricating such a lens withpart thereof cut away may include, for example, the following methodscan be used as appropriate: a method in which a mold having apredetermined forming surface (forming surface that allows a lens withpart thereof cut away to be fabricated) is used to carry out injectionmolding, and a method in which a rotationally symmetric lens(cylindrical lens) is temporarily fabricated and part of the lens is cutaway.

The reflective light guiding system 640 includes a reflection mirror 642as a first reflection element disposed on the light-exiting side of thefirst lens group 610, a reflection mirror 644 as a second reflectionelement disposed above the reflection mirror 642, and a reflectionmirror 646 as a third reflection element disposed between the reflectionmirror 644 and the second lens group 620. The reflective light guidingsystem 640 has a function of reflecting the light from the first lensgroup 610 in a predetermined direction containing the upward direction(z(+) direction) as a vector component and guiding the reflected lightto the curved mirror 630. Each of the reflection mirrors 642, 644, and646 has a flat reflection plane.

The reflection mirror 642 is disposed in such a way that a normal to thereflection plane thereof is inclined by 45 degrees to the optical axisof the first lens group 610. The thus disposed reflection mirror 642reflects the light that exits from the first lens group 610 (the lightoriented in the y (+) direction) upward (in the z (+) direction).

The reflection mirror 644 is disposed in such a way that a normal to thereflection plane of the reflection mirror 644 is perpendicular to anormal to the reflection plane of the reflection mirror 642. The thusdisposed reflection mirror 644 reflects the light reflected off thereflection mirror 642 (the light oriented in the z (+) direction) in they (−) direction.

The reflection mirror 646 is disposed above the first lens group 610 insuch a way that a normal to the reflection plane of the reflectionmirror 646 is inclined by 45 degrees to the central axis of the lightreflected off the reflection mirror 644. The thus disposed reflectionmirror 646 reflects the light reflected off the reflection mirror 644(the light oriented in the y (−) direction) in the x (+) direction.

The reflection mirrors 642, 644, and 646 are adjusted in terms of layoutposition and angle and then fixed to a fixing member (not shown). Thatis, the reflective light guiding system 640 is configured as a unitstructure in which the reflection mirrors 642, 644, and 646 areintegrated.

The curved mirror 630 is a concave mirror and disposed with its layoutposition and angle adjusted in such a way that the light that exits fromthe second lens group 620 is projected on the screen SCR. The curvedmirror 630 is also disposed in such a way that the optical axis of thecurved mirror 630 is twisted with respect to the optical axis of thefirst lens group 610, that is, the optical axis of the curved mirror 630does not intersect the optical axis of the first lens group 610 (seeFIG. 1).

The optical axis of the curved mirror 630 means the central axis ofrotation around which the concave plane of the curved mirror 630 isrotated to form a rotationally symmetric body.

The thus configured projection system 600 enlarges and projects a colorimage that exits from the cross dichroic prism 500 to form alarge-screen image on the screen SCR.

A description will be made of the relationship between a projectionimage projected on the screen SCR and the reflective type of liquidcrystal panels 400R, 400G, and 400B in the projector 1000 according tothe first embodiment with reference to FIGS. 4A to 4D.

FIGS. 4A to 4D explain the relationship between a projection image IMGprojected on the screen SCR and the reflective type of liquid crystalpanels 400R, 400G, and 400B. FIG. 4A shows the screen SCR viewed fromthe front (the x (+) direction). FIG. 4B shows the reflective type ofliquid crystal panel 400R viewed from the front (the y (−) direction).FIG. 4C shows the reflective type of liquid crystal panel 400G viewedfrom the front (the x (−) direction). FIG. 4D shows the reflective typeof liquid crystal panel 400B viewed from the front (the y (−)direction). The size of the screen SCR shown in FIG. 4A and the sizes ofthe reflective type of liquid crystal panels 400R, 400G, and 4003 shownin FIGS. 4B to 4D are exaggerated.

The projection image IMG projected on the screen SCR is a wide-visionimage having an aspect ratio of 16:9. As shown in FIG. 4A, thelongitudinal direction of the projection image IMG extends along the ydirection, and the short-side direction extends along the z direction.

On the other hand, the reflective type of liquid crystal panels 400R,400G, and 400B are disposed, as shown in FIGS. 4B to 4D, in such a waythat the longitudinal directions of the image formation areas S_(R),S_(G), and S_(B) extend along the x or y direction (do not extend alongthe z direction).

Before describing the projector 1000 according to the first embodimentin more detail, a projector 1000 a according to a comparative example(related art) of the first embodiment will be described.

FIG. 5 is an overall perspective view showing the optical system of theprojector 1000 a according to the comparative example. FIG. 6 explainsthe projector 1000 a according to the comparative example. In FIG. 6,the optical path folded at a reflection mirror 642 a is unfolded inorder to illustrate two-dimensionally the positional relationship alongthe z direction among the optical components present in the area betweenreflective type of liquid crystal panels 400R, 400G, 400B and a curvedmirror 630.

In FIG. 5, the same members as those in FIG. 1 have the same referencecharacters and no detailed description of such members will be made.

The projector 1000 a according to the comparative example is basicallyconfigured in a manner quite similar to the projector 1000 according tothe first embodiment, but differs therefrom in terms of theconfiguration of the reflective light guiding system.

As the reflective light guiding system, the projector 1000 a accordingto the comparative example includes, as shown in FIG. 5, a reflectivelight guiding system 640 a disposed between a first lens group 610 and asecond lens group 620, the reflective light guiding system 640 areflecting the light from the first lens group 610 in the x (+)direction as a third direction and guiding the reflected light to thecurved mirror 630. The curved mirror 630 is disposed in such a way thatthe optical axis of the curved mirror 630 intersects the optical axis ofthe first lens group 610.

The reflective light guiding system 640 a includes the reflection mirror642 a disposed on the light-exiting side of the first lens group 610 insuch a way that a normal to the reflection plane of the reflectionmirror 642 a is inclined by 45 degrees to the optical axis of the firstlens group 610. The thus disposed reflection mirror 642 a reflects thelight that exits from the first lens group 610 (the light oriented inthe y (+) direction) sideward (in the x (+) direction).

In the positional relationship along the z direction among the opticalcomponents present in the area between the reflective type of liquidcrystal panels 400R, 400G, 400B and the curved mirror 630 in theprojector 1000 a according to the comparative example, as seen from FIG.6, the first lens group 610, the second lens group 620, and the curvedmirror 630 are disposed in such a way that the optical axis A2 of thefirst lens group 610, the optical axis A3 of the second lens group 620,and the optical axis A4 of the curved mirror 630 are shifted downward(in the z(−) direction) from the central axis A1 of the image formationareas of the reflective type of liquid crystal panels 400R, 400G, and4003. Further, the optical axis A2 of the first lens group 610, theoptical axis A3 of the second lens group 620, and the optical axis A4 ofthe curved mirror 630 are configured to be present in the same plane.

Since the thus configured projector 1000 a according to the comparativeexample includes the reflective light guiding system 640 a configured asdescribed above, the space in which a projection system 600 a isdisposed can be reduced (more compact) as compared to that in relatedart, whereby the projector 1000 a can be more compact. In this case,however, since the curved mirror 630 is disposed in a position shifteddownward (in the z(−) direction) from the reflective type of liquidcrystal panels 400R, 400G, and 400B (first lens group 610), part of thelight reflected off the curved mirror 630 may disadvantageously hit anoptical system and other components. To prevent the light reflected offthe curved mirror 630 from hitting the optical system, for example, thelocation where the optical system and other components are disposed mustbe changed, which is not preferable because the degrees of freedom inproduct design are reduced.

In contrast, in the projector 1000 according to the first embodiment,since the reflective light guiding system 640 comprised of threereflection mirrors 642, 644, and 646 is disposed along the optical pathbetween the first lens group 610 and the curved mirror 630, the lightfrom the first lens group 610 can be bent three times and guided to thecurved mirror 630. As a result, the space in which the projection system600 is disposed can be reduced (more compact) as compared to the case,for example, in the configuration of a projector of related art, wherethe light from the first lens group is not bent at all but directlyguided to the curved mirror, whereby the projector 1000 can be morecompact.

FIG. 7 explains the projector 1000 according to the first embodiment. InFIG. 7, part of the folded optical path is unfolded, as in FIG. 6, inorder to illustrate two-dimensionally the positional relationship alongthe z direction among the optical components present in the area betweenthe reflective type of liquid crystal panels 400R, 400G, 400B and thecurved mirror 630.

In the projector 1000 according to the first embodiment, as seen fromFIG. 7, the first lens group 610 is disposed in such a way that theoptical axis A2 of the first lens group 610 is shifted downward (in thez (−) direction) from the central axis A1 of the image formation areasof the reflective type of liquid crystal panels 400R, 400G, and 400B.The second lens group 620 and the curved mirror 630 are disposed in sucha way that the optical axis A3 of the second lens group 620 and theoptical axis A4 of the curved mirror 630 are shifted upward (in the z(+)direction) from the optical axis A2 of the first lens group 610. Inother words, the optical axis A3 of the second lens group 620 and theoptical axis A4 of the curved mirror 630 are present in the same plane,but the optical axis A2 of the first lens group 610 is not present inthat plane.

Therefore, in the projector 1000 according to the first embodiment,since the curved mirror 630 is disposed in a position shifted upward (inthe z(+) direction) from the reflective type of liquid crystal panels400R, 400G, and 400B (first lens group 610), the light reflected off thecurved mirror 630 will not hit the optical system. It is thereforepossible to achieve a projector in which a large number of degrees offreedom are available in product design.

In the projector 1000 according to the first embodiment, since thereflection mirrors 642, 644, and 646 that form the reflective lightguiding system 640 have flat reflection planes, the structure of thereflective light guiding system 640 is simpler and the reflectionmirrors can be smaller than in the case where the reflection planes arecurved. Such an advantage contributes to reduction in size of theproduct.

In the projector 1000 according to the first embodiment, since theoptical axis A2 of the first lens group 610 does not intersect theoptical axis A4 of the curved mirror 630, it is possible to achieve aprojector in which a large number of degrees of freedom are available inproduct design.

In the projector 1000 according to the first embodiment, two of theoptical axis A2 of the first lens group 610, the optical axis A3 of thesecond lens group 620, and the optical axis A4 of the curved mirror 630(the optical axis A3 of the second lens group 620 and the optical axisA4 of the curved mirror 630 in the first embodiment) are present in thesame plane, but the one remaining optical axis (the optical axis A2 ofthe first lens group 610 in the first embodiment) is not present in thatplane. Such a configuration allows the space in the projector 1000 to beeffectively used and the projector 1000 to be more compact, readilyprevents the light reflected off the curved mirror 630 from hitting theoptical system, and allows a projector in which a large number ofdegrees of freedom are available in product design to be achieved.

In the projector 1000 according to the first embodiment, since thereflective light guiding system 640 is configured as a unit structure inwhich the three reflection mirrors 642, 644, and 646 are integrated, theapparatus is readily assembled.

In the projector 1000 according to the first embodiment, since each ofthe first lens group 610 and the second lens group 620 is configured asa unit structure in which a plurality of lenses are integrated, theapparatus is readily assembled.

In the projector 1000 according to the first embodiment, since thereflective light guiding system 640 includes the reflection mirrors 642,644, and 646 disposed and configured as described above, it is possibleto readily achieve a projector that is more compact and has a largernumber of degrees of freedom in product design than related art.

In the projector 1000 according to the first embodiment, since each ofthe reflection elements in the reflective light guiding system 640 is areflection mirror, the light from the first lens group 610 can bereliably guided to the curved mirror 630. Further, the manufacturingcost of the projector 1000 can be reduced as compared to a case wherethe reflection elements are reflection prisms.

In the projector 1000 according to the first embodiment, since thecurved mirror 630 is a concave mirror, the product height of theprojector 1000 can be lower than in a case where the curved mirror is,for example, a convex mirror.

In the projector 1000 according to the first embodiment, the lenses L1and L2 that form the second lens group 620 are shaped in such a way thatpart of the lenses L1 and L2 on the upper (z(+) direction) side withrespect to the lens optical axis thereof is cut away. Such aconfiguration allows the weight of the lenses to be reduced and thespace in the projector 1000 to be effectively used. Further, since theportions cut away from the lenses L1 and L2 are regions through whichthe light reflected off the reflection mirror 646 does not pass, thereare no problems resulting from the cutting, for example, no lightguiding path.

Second to Fourth Embodiments

In second to fourth embodiments, cases where the reflective lightguiding system includes two reflection elements are described.

FIG. 8 is an overall perspective view showing the optical system of aprojector 1002 according to the second embodiment. FIGS. 9A and 9Bexplain a projection system 602. FIG. 9A is a top view of the projectionsystem 602 (viewed from the z (+) direction). FIG. 9B is a side view ofthe projection system 602 (viewed from the x (−) direction).

FIG. 10 is an overall perspective view showing the optical system of aprojector 1004 according to the third embodiment. FIGS. 11A and 11Bexplain a projection system 604. FIG. 11A is a top view of theprojection system 604 (viewed from the z (+) direction). FIG. 11B is aside view of the projection system 604 (viewed from the x (−)direction).

FIG. 12 is an overall perspective view showing the optical system of aprojector 1006 according to the fourth embodiment. FIGS. 13A and 13Bexplain a projection system 606. FIG. 13A is a top view of theprojection system 606 (viewed from the z (+) direction). FIG. 13B is aside view of the projection system 606 (viewed from the x (−)direction).

In FIGS. 8 to 13A and 13B, the same members as those in FIGS. 1, 3A, and3B have the same reference characters and no detailed description ofsuch members will be made. In FIGS. 8 to 13A and 13B, a plurality oflenses that form a first lens group 610 and a second lens group 620 areabstractly illustrated.

FIGS. 14A to 14D explain the relationship between a projection image IMGprojected on a screen SCR and reflective type of liquid crystal panels400R, 400G, and 400B in the second to fourth embodiments. FIG. 14A showsthe screen SCR viewed from the front (the x (+) direction). FIG. 14Bshows the reflective type of liquid crystal panel 400R viewed from thefront (the y (−) direction). FIG. 14C shows the reflective type ofliquid crystal panel 400G viewed from the front (the x (−) direction).FIG. 14D shows the reflective type of liquid crystal panel 400B viewedfrom the front (the y (−) direction).

The size of the screen SCR shown in FIG. 14A and the sizes of thereflective type of liquid crystal panels 400R, 400G, and 400B shown inFIGS. 14B to 14D are exaggerated. In FIGS. 14A to 14D, the same membersas those in FIGS. 4A to 4D have the same reference characters and nodetailed description of such members will be made.

The projectors 1002 1004 and 1006 according to the second to fourthembodiments basically have configurations similar to that of theprojector 1000 according to the first embodiment but differ therefrom interms of the configuration of the projection system.

That is, the projector 1002 according to the second embodiment includesas the projection system, as shown in FIGS. 8, 9A, and 9B, theprojection system 602 having a first lens group 610, a second lens group622 disposed on the light-exiting side of the first lens group 610, acurved mirror 630 disposed on the light-exiting side of the second lensgroup 622, and a reflective light guiding system 650 disposed along theoptical path from the first lens group 610 to the curved mirror 630. Thesecond lens group 622 is disposed in such a way that the optical axis ofthe second lens group 622 extends along the z direction. The second lensgroup 622 has substantially the same configuration as that of the secondlens group 620 described in the first embodiment, but differs therefromin that part of the lenses that form the second lens group 622 is notcut away.

The reflective light guiding system 650 includes a reflection mirror 652as a first reflection element disposed between the first lens group 610and the second lens group 622, and a reflection mirror 654 as a secondreflection element disposed between the second lens group 622 and thecurved mirror 630. The reflective light guiding system 650 has afunction of reflecting the light from the first lens group 610 in apredetermined direction containing the upward direction (z(+) direction)as a vector component and guiding the light to the curved mirror 630.Each of the reflection mirrors 652 and 654 has a flat reflection plane.

The reflection mirror 652 is disposed in such a way that a normal to thereflection plane thereof is inclined by 45 degrees to the optical axisof the first lens group 610. The thus disposed reflection mirror 652reflects the light that exits from the first lens group 610 (the lightoriented in the y (+) direction) upward (in the z (+) direction).

The reflection mirror 654 is disposed above the second lens group 622 insuch a way that a normal to the reflection plane of the reflectionmirror 654 is inclined by 45 degrees to the central axis of the lightthat exits from the second lens group 622. The thus disposed reflectionmirror 654 reflects the light that exits from the second lens group 622(the light oriented in the z (+) direction) in the x (+) direction.

The projector 1004 according to the third embodiment includes as theprojection system, as shown in FIGS. 10, 11A, and 11B, the projectionsystem 604 having a first lens group 610, a second lens group 620disposed on the light-exiting side of the first lens group 610, a curvedmirror 630 disposed on the light-exiting side of the second lens group620, and a reflective light guiding system 660 disposed between thefirst lens group 610 and the second lens group 620. The second lensgroup 620 is disposed in such a way that the optical axis of the secondlens group 620 extends along the x direction.

The reflective light guiding system 660 includes a reflection mirror 662as a first reflection element disposed on the light-exiting side of thefirst lens group 610, and a reflection mirror 664 as a second reflectionelement disposed between the reflection mirror 662 and the second lensgroup 620. The reflective light guiding system 660 has a function ofreflecting the light from the first lens group 610 in a predetermineddirection containing the upward direction (z(+) direction) as a vectorcomponent and guiding the light to the curved mirror 630. Each of thereflection mirrors 662 and 664 has a flat reflection plane.

The reflection mirror 662 is disposed in such a way that a normal to thereflection plane thereof is inclined by 45 degrees to the optical axisof the first lens group 610. The thus disposed reflection mirror 662reflects the light that exits from the first lens group 610 (the lightoriented in the y (+) direction) upward (in the z (+) direction).

The reflection mirror 664 is disposed above the reflection mirror 662 insuch a way that a normal to the reflection plane of the reflectionmirror 664 is inclined by 45 degrees to the central axis of the lightreflected off the reflection mirror 662. The thus disposed reflectionmirror 664 reflects the light reflected off the reflection mirror 662(the light oriented in the z (+) direction) in the x (+) direction.

In the third embodiment, the size of the projector 1004 is reduced byreducing the distance between the reflection mirror 662 and thereflection mirror 664 to the smallest possible distance.

The projector 1006 according to the fourth embodiment includes as theprojection system, as shown in FIGS. 12, 13A, and 133, the projectionsystem 606 having a first lens group 610, a lens group 680 disposed onthe light-exiting side of the first lens group 610, a curved mirror 630disposed on the light-exiting side of the lens group 680, and areflective light guiding system 670 disposed along the optical path fromthe first lens group 610 and the curved mirror 630. The lens group 680includes a second lens group 682 and a third lens group 684. Each of thetwo lens groups 682 and 684 is configured as a unit structure in which aplurality of lenses are integrated. The second lens group 682 isdisposed in such a way that the optical axis of the second lens group682 extends along the z direction, and the third lens group 684 isdisposed in such a way that the optical axis of the third lens group 684extends along the x direction.

The reflective light guiding system 670 includes a reflection mirror 672as a first reflection element disposed on the light-exiting side of thefirst lens group 610, and a reflection mirror 674 as a second reflectionelement disposed between the second lens group 682 and the third lensgroup 684. The reflective light guiding system 670 has a function ofreflecting the light from the first lens group 610 in a predetermineddirection containing the upward direction (z(+) direction) as a vectorcomponent and guiding the light to the curved mirror 630. Each of thereflection mirrors 672 and 674 has a flat reflection plane.

The reflection mirror 672 is disposed in such a way that a normal to thereflection plane thereof is inclined by 45 degrees to the optical axisof the first lens group 610. The thus disposed reflection mirror 672reflects the light that exits from the first lens group 610 (the lightoriented in the y (+) direction) upward (in the z (+) direction).

The reflection mirror 674 is disposed above the second lens group 682 insuch a way that a normal to the reflection plane of the reflectionmirror 674 is inclined by 45 degrees to the central axis of the lightthat exits from the second lens group 682. The thus disposed reflectionmirror 674 reflects the light that exits from the second lens group 682(the light oriented in the z (+) direction) in the x (+) direction.

The projectors 1002 to 1006 according to the second to fourthembodiments not only differ from the projector 1000 according to thefirst embodiment in terms of the configuration of the projection systemas described above, but also differ from the projector 1000 according tothe first embodiment in terms of the layout of the reflective type ofliquid crystal panels.

That is, in the projectors 1002 to 1006 according to the second tofourth embodiments, as shown in FIGS. 8, 10, and 12, each of thereflective type of liquid crystal panels 400R, 400G, and 400B is rotatedby 90 degrees around the central axis of the image formation area as theaxis of rotation in such a way that the longitudinal direction of theimage formation area extends along the z direction.

Referring to FIGS. 14A to 14D, a projection image IMG projected on thescreen SCR is a wide-vision image having an aspect ratio of 16:9, as inthe first embodiment. As shown in FIG. 14A, the projection image IMG isformed in such a way that the longitudinal direction extends along the ydirection and the short-side direction extends along the z direction. Onthe other hand, the reflective type of liquid crystal panels 400R, 400G,and 400B are disposed, as shown in FIGS. 14B to 14D, in such a way thatthe longitudinal directions of the image formation areas S_(R) S_(G),and S_(B) extend along the z direction (do not extend along the x or ydirection).

In the projectors 1002 to 1006 according to the second to fourthembodiments, not only is the layout of the reflective type of liquidcrystal panels 400R, 400B, and 400G changed, but also the layout of thefirst lens array 120, the second lens array 130, and the polarizationconversion element 140 in the illumination system 100 is changed.Specifically, as shown in FIGS. 8, 10, and 12, the first lens array 120,the second lens array 130, and the polarization conversion element 140are rotated by 90 degrees around the respective central axes of theabove optical members as the axes of rotation.

As described above, although the projectors 1002 to 1006 according tothe second to fourth embodiments differ from the projector 1000according to the first embodiment in terms of the configuration of theprojection system, the layout of the reflective type of liquid crystalpanels, and the layout of part of the optical components in theillumination system, the projectors 1002 to 1006 include the reflectivelight guiding systems 650 to 70 having the two respective reflectionmirrors 652, 654, 662, 664, 672, and 674 as reflection elements,reflecting the light from the first lens group 610 in a predetermineddirection containing the upward direction (z(+) direction) as a vectorcomponent, and guiding the light to the curved mirror 630, as in theprojector 1000 according to the first embodiment, whereby the spaces inwhich the projection systems 602 to 606 are disposed can be smaller(more compact) and hence the projectors 1002 to 1006 can be more compactthan projectors of related art.

As described above, the projectors 1002 to 1006 according to the secondto fourth embodiments are configured in such a way that the longitudinaldirection of the projection image IMG projected on the screen SCR (ydirection) does not coincide with the longitudinal directions of theimage formation areas S_(R), S_(G), and S_(B) of the reflective type ofliquid crystal panels 400R, 400G, and 400B (z direction), because in theprojection system 600 of the projector 1000 according to the firstembodiment, the light oriented in the z(+) direction is temporarilyreflected off the reflection mirror 644 in the y(−) direction and thenreflected off the reflection mirror 646 in the x(+) direction, while inthe projection systems 602, 604, and 606 of the projectors 1002 to 1006according to the second to fourth embodiments, the light oriented in thez(+) direction is reflected off the reflection mirrors 654, 664, and 674directly in the x(+) direction. In the thus configured projectors 1002to 1006 according to the second to fourth embodiments, when the opticalsystems from the illumination system 100 to the cross dichroic prism 500are disposed in such a way that the system optical axis of the opticalsystems from the illumination system 100 to the cross dichroic prism 500extends along the x-y plane, disposing the reflective type of liquidcrystal panels 400R, 400G, and 400B in such a way that the longitudinaldirections of the image formation areas S_(R), S_(G), and S_(B) extendalong the z direction allows the images of the vertically elongatedreflective type of liquid crystal panels 400R, 400G, and 400B to becorrectly projected on the screen SCR as projection images IMG whoselongitudinal directions extend along the y direction. Since disposingthe reflective type of liquid crystal panels 400R, 400G, and 400B insuch a way that the image formation areas S_(R), S_(G), and S_(B) arevertically elongated (elongated along the z direction) allows the sizesof the cross dichroic prism 500 in the x and y directions to be reducedas compared to a case where the reflective type of liquid crystal panels400R, 400G, and 400B are disposed in such a way that the image formationareas S_(R), S_(G), and S_(B) are horizontally elongated (elongatedalong the x or y direction), the length of the optical path in the colorseparation/light guiding system 200 is reduced, whereby the back focaldistances of the projection systems 602 to 606 can be reduced and hencethe sizes of the projection systems 602 to 606 can be advantageouslyfurther reduced.

Each of the projection systems 602 to 606 in the second to fourthembodiments can also be used to project a projection image IMG whoselongitudinal direction extends along the y direction on the screen SCRnot only by disposing the optical systems from the illumination system100 to the cross dichroic prism 500 in such a way that color separationin the color separation/light guiding system 200 is performed along thevertical direction (z direction) and the system optical axis of theoptical systems from the illumination system 100 to the cross dichroicprism 500 extends along the y-z plane but also by disposing thereflective type of liquid crystal panels 400R, 400G, and 400B in such away that the longitudinal directions of the image formation areas S_(R)S_(G), and S_(B) extend along the z direction. In this case, however, inthe entire optical system from the illumination system 100 to each ofthe projection systems 602 to 606, the lengths along the x and ydirections will not be greatly reduced, but the length along the zdirection disadvantageously increases.

In contrast, in each of the projectors 1002 to 1006 according to thesecond to fourth embodiments, since not only are the optical systemsfrom the illumination system 100 to the cross dichroic prism 500disposed in such a way that color separation in the colorseparation/light guiding system 200 is performed along the horizontaldirection (x or y direction) and the system optical axis from theillumination system 100 to the cross dichroic prism 500 extends alongthe x-y plane, but also the reflective type of liquid crystal panels400R, 400G, and 400B are disposed in such a way that the longitudinaldirections of the image formation areas S_(R), S_(G), and S_(B) extendalong the z direction, each of the projection systems 602 to 606 canproject a horizontally elongated projection image IMG (whoselongitudinal direction is parallel to the y direction) on the screen SCRwhile the length of the entire optical system from the illuminationsystem 100 to each of the projection systems 602 to 606 along the zdirection does not increase but remains compact.

Since the projectors 1002 to 1006 according to the second to fourthembodiments have a configuration similar to that of the projector 1000according to the first embodiment but only differ therefrom in terms ofthe configuration of the projection system, the layout of the reflectivetype of liquid crystal panels, and the layout of part of the opticalcomponents in the illumination system, the projectors 1002 to 1006 haverelevant advantageous effects of those provided in the projector 1000according to the first embodiment.

While the projectors of some aspects of the invention have beendescribed with reference to the above embodiments, the invention is notlimited thereto, but can be implemented in a variety of aspects to theextent that they do not depart from the spirit of the invention. Forexample, the following variations are possible.

In the above embodiments, the description has been made with referenceto the case where the number of reflection elements that form thereflective light guiding system is two or three, but the invention isnot limited thereto. The number of reflection elements may be four orgreater.

In the above embodiments, the description has been made with referenceto the case where the reflection elements that form the reflective lightguiding system are reflection mirrors, but the invention is not limitedthereto. The reflection elements may be reflection prisms.

In the above embodiments, the description has been made with referenceto the case where the curved mirror is a concave mirror, but theinvention is not limited thereto. For example, the curved mirror may bea convex mirror or a free-form curved mirror.

In the first to third embodiments, the second lens group includes twolenses, but the invention is not limited thereto. The second lens groupmay include three or more lenses. In the fourth embodiment, each of thesecond lens group 682 and the third lens group 684 includes a pluralityof lenses, but the invention is not limited thereto. One or both of thelens groups may be comprised of a single lens.

In the first embodiment, the description has been made with reference tothe case where each of the reflective type of liquid crystal panels isdisposed in such a way that the longitudinal direction of the imageformation area extends along the x or y direction, whereas in the secondto fourth embodiments, the description has been made with reference tothe case where each of the reflective type of liquid crystal panels isdisposed in such a way that the longitudinal direction of the imageformation area extends along the z direction and the reflective type ofliquid crystal panel is rotated from the state in the first embodimentby 90 degrees around the central axis of the image formation area as theaxis of rotation. The invention, however, is not limited thereto. Eachof the reflective type of liquid crystal panels may be disposed in sucha way that the reflective type of liquid crystal panel is rotated fromthe state in the first embodiment, for example, by 45 degrees around thecentral axis of the image formation area as the axis of rotation. Inthis case, the optical components of the projection system arepreferably configured in such a way that a projection image projected onthe screen is horizontally elongated.

In the above embodiments, a wide-vision reflective type of liquidcrystal panel in which the image formation area has an aspect ratio of16:9 is used as the reflective type of liquid crystal panel, but theinvention is not limited thereto. What is called a standard reflectivetype of liquid crystal panel in which the image formation area has anaspect ratio of 4:3 may be used.

In the above embodiments, a light source including an ellipsoidalreflector is used as the light source, but the invention is not limitedthereto. A light source including a parabolic reflector may also bepreferably used. In this case, no concave lens is required.

In the above embodiments, the description has been made with referenceto the case where a sub-mirror is provided in the arc tube, but theinvention is not limited thereto. The sub-mirror may be replaced with areflection film formed on the outer surface of the lamp body, or theinvention is applicable to a projector with no sub-mirror disposedtherein.

In the above embodiments, a lens integrator system comprised of a lensarray is used as a light homogenizing system, but the invention is notlimited thereto. A rod integrator system comprised of rod members canalso be preferably used.

In the above embodiments, a plate-type polarizing beam splitter is usedas the polarizing beam splitter in the color separation/light guidingsystem, but the invention is not limited thereto. A prism-typepolarizing beam splitter in which two triangular prisms are bonded maybe used.

In the above embodiments, the description has been made with referenceto the projector using three reflective type of liquid crystal panels,but the invention is not limited thereto. The invention is alsoapplicable to a projector using one reflective type of liquid crystalpanel, a projector using two reflective type of liquid crystal panels,and a projector using four or more reflective type of liquid crystalpanels.

In the above embodiments, the description has been made with referenceto a reflective type projector, but the invention is not limitedthereto. The invention is also applicable to a transmissive typeprojector. The word “reflective” used herein means that theelectro-optic modulator as the light modulator is of light-reflectingtype, such as a reflective type of liquid crystal panel, and the word“transmissive” used herein means that the electro-optic modulator as thelight modulator is of light-transmitting type, such as a transmissivetype of liquid crystal panel. When the invention is applied to atransmissive type projector, the same advantageous effects as thoseprovided in a reflective type projector can also be provided.

In the above embodiments, a reflective type of liquid crystal panel isused as the electro-optic modulator, but the invention is not limitedthereto. In general, the electro-optic modulator may be any other devicethat modulates incident light according to image information, such as amicromirror light modulator. For example, a DMD (Digital MicromirrorDevice: a trademark of Texas Instruments) can be used as the micromirrorlight modulator.

The invention is applicable not only to a front projection typeprojector that projects a projection image from the observation side butalso to a rear projection type projector that projects a projectionimage from the side opposite the observation side.

The invention is applicable not only to a projector installed on a deskor other surfaces (desktop type projector) but also to a projectorhanging from the ceiling or other surfaces (ceiling-hanging typeprojector).

1. A projection optical system comprising: a plurality of lens groups including at least a first lens group and a second lens group, and a curved plane mirror, wherein the projection optical system includes a two story structure having a first story located below a second story in a first direction, and includes a plurality of plane mirrors that bends at least two times the light incident from a color combining system disposed upstream of the light path of the projection optical system, the plurality of plane mirrors including a first plane mirror disposed between the first lens group and the second lens group, the first plane mirror reflecting the light from the first lens group in a second direction that is opposite the first direction, a second plane mirror disposed between the first plane mirror and the second lens group in such a way that a normal to a reflection plane of the second plane mirror is perpendicular to a normal to a reflection plane of the first plane mirror, and a third plane mirror disposed between the second plane mirror and the second lens group, the third plane mirror reflecting the light from the second plane mirror toward the second lens group.
 2. The projection optical system according to claim 1, wherein the projection optical system comprises: the first lens group, first, second and third plane mirrors, second lens group and the curved plane mirror being arranged in order from upstream to downstream of the light path. 